Solvent-resistant textile binder

ABSTRACT

The invention provides a process for improving the resistance to solvents in finishing and stabilizing fiber materials with textile binders, wherein the textile binder used is an aqueous copolymer dispersion or a redispersible copolymer powder of copolymers with a T g  of -60° C. to +60° C., containing (a) one or more monomer units from the group consisting of vinyl esters of unbranched or branched carboxyli acids with 1 to 12 carbon atoms, esters of acrylic acid and methacrylic acid with unbranched or branched alcohols with 1 to 12 carbon atoms, vinyl aromatics, vinyl halides and α-olefins, and (b) 0.3 to 10 wt %, relative to the total weight of the copolymer, of one or more N-(alkoxymethyl)-acrylamides or N-(alkoxymethyl)methacrylamides with a C 1  -C 6  alkyl residue, or mixtures of these N-(alkoxymethyl)-meth(acrylamides with N-Methylolacrylamide and/or N-methylolmethacrylamide in a weight ratio of N-methylol compound to N-(alkoxymethyl) compound of at most 5:1.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The invention relates to the use of N-(alkoxymethyl)(meth)acrylamide-functional textile binders for improving the resistanceto solvents in the finishing and bonding of fiber materials, and to aprocess for the preparation of solvent-resistant fiber structures.

2) Background Art

The use of aqueous copolymer dispersions as binders for bonding andcoating fiber structures such as woven fabrics, nonwovens and waddingsof textile fiber or textile yarns is known. Copolymer dispersions of(meth)acrylate or vinyl ester copolymers which compriseself-crosslinking comonomer units with N-methylol or N-methylol etherfunctions to improve their strength are often used here. Up to 10% byweight of N-methylol(meth)acrylamide (NMA or NMMA) are usuallycopolymerized. Disadvantages of these binders are the release offormaldehyde due to hydrolytic cleavage of the N-methylol function andthe low resistance to solvents of the materials bonded or coated withthem. Improvement of the resistance to solvents by incorporation ofprecrosslinking, poly-ethylenically unsaturated comonomer units isknown. However, this measure often leads to problems in the preparationof the copolymers.

Thermally self-crosslinking copolymers which comprise 2 to 10% by weightof N-methylol(meth)acrylamide or the N-methylol ether thereof are knownfrom DE-A 2512589 (U.S. Pat. No. 4,044,197). A disadvantage is that,although in the case of the N-methylolacrylamide-containing copolymersused therein the heat-treated copolymer films show a good resistance tosolvents, the nonwovens bonded with them do not.

EP-B 205862 relates to textile binders based on vinyl acetate/ethylenecopolymers which comprise 1 to 5% by weight ofN-methylol(meth)acrylamide units or ethers thereof. To improve the wetstrength if a copolymer binder of low NMA content is used, theadditional use of melamine-formaldehyde resins is proposed.

The doctrine of EP-A 261378 is to improve the heat stability of fibermats bonded with N-methylol-functional copolymers by employing asbinders those copolymers in which the N-methylol functions arecompletely or partly etherified.

WO-A 92/08835 describes textile binders based on vinyl acetate/ethylenecopolymer emulsions which comprise exclusivelyN-(n-butoxymethyl)acrylamide units instead of N-methylol(meth)acrylamideunits to reduce the release of formaldehyde.

EP-A 86889 (AU-A 8310718) relates to a process for the preparation of atextile coating composition which shows no white swelling and no whitefracture under the action of water. The coating composition comprises anaqueous copolymer emulsion which is obtained by emulsioncopolymerization of (meth)acrylates with N-methylol(meth)acrylamide, theN-methylol(meth)acrylamides being etherified to the extent of at least20 mol % with an alcohol and the emulsion polymerization being carriedout in the presence of a fatty alcohol having 10 to 20 C atoms. Theresistance of textile binders to solvents is not discussed.

SUMMARY OF THE INVENTION

The invention was based on the object of providing binders based onaqueous copolymer dispersions or copolymer powders which impart totextiles finished with them a high resistance to solvents, in additionto a high dry and wet strength.

Surprisingly, this has been achieved by using, instead ofN-methylol-functional copolymers, those in which some of the N-methylolfunctions are etherified, with which the opposite effect was rather tobe expected because of the hydrophobic character of the copolymerscontaining N-methylol ethers.

The invention relates to the use ofN-(alkoxymethyl)(meth)acrylamide-functional textile binders forimproving the resistance to solvents in the finishing and bonding offiber materials with textile binders, which comprises using as thetextile binder an aqueous copolymer dispersion or a redispersiblecopolymer powder of copolymers having a T_(g) of -60° C. to +60° C.comprising

a) one or more monomer units from the group consisting of vinyl estersof unbranched or branched carboxylic acids having 1 to 12 C atoms,esters of acrylic acid and methacrylic acid with unbranched or branchedalcohols having 1 to 12 C atoms, vinylaromatics, vinyl halides andα-olefins and

b) 0.3 to 10% by weight, based on the total weight of the copolymer, ofa mixture of monomer units of one or more N-(alkoxymethyl)acrylamides orN-(alkoxymethyl)methacrylamides with a C₁ - to C₆ -alkyl radical withN-methylolacrylamide and/or N-methylolmethacrylamide in a weight ratioof N-methylol compound to N-(alkoxymethyl) compound of not more than5:1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred N-(alkoxymethyl) (meth)acrylamides areN-(isobutoxymethyl)acrylamide (IBMA), N-(isobutoxymethyl)methacrylamide(IBMMA), N-(n-butoxymethyl)acrylamide (NBMA) andN-(n-butoxymethyl)methacrylamide (NBMMA).

The copolymers preferably comprise 0.5 to 3.0% by weight, based on thetotal weight of the copolymer, of a mixture of monomer units ofN-(alkoxymethyl)acrylamides or N-(alkoxymethyl)methacrylamides with aC₁ - to C₆ -alkyl radical with N-methylolacrylamide (NMA) and/orN-methylolmethacrylamide (NMMA). Copolymers which comprise, in theweight contents mentioned, mixtures of the N-(alkoxymethyl)(meth)acrylamides with N-methylolacrylamide or N-methylolmethacrylamidein a weight ratio of N-methylol compound to N-(alkoxymethyl) compound of5:1 to 1:10 are particularly preferred. Copolymers which comprise 0.5 to3.0% by weight, based on the total weight of the copolymer, of a mixtureof NMA and IBMA (IBMMA) in a weight ratio of NMA/IBMA (IBMMA) of 3:1 to1:5, in particular 1:1 to 1:5, are most preferred.

Preferred vinyl esters are vinyl acetate, vinyl propionate, vinylbutyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate,vinyl pivalate and vinyl esters of α-branched monocarboxylic acidshaving 9 or 10 C atoms, for example VeoVa9® or VeoVa10® (Shellcorporation's vinyl esters of versatic acids). Vinyl acetate isparticularly preferred.

Preferred methacrylic acid esters or acrylic acid esters are methylacrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate,propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butylmethacrylate and 2-ethylhexyl acrylate. Methyl acrylate, methylmethacrylate, n-butyl acrylate and 2-ethylhexyl acrylate areparticularly preferred.

The vinyl ester copolymers can comprise, if appropriate, 1.0 to 50% byweight, based on the total weight of the comonomer phase, of α-olefins,such as ethylene or propylene, and/or vinylaromatics, such as styrene,and/or vinyl halides, such as vinyl chloride, and/or acrylic acid estersor methacrylic acid esters of alcohols having 1 to 12 C atoms, such asmethyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate,n-butyl methacrylate and 2-ethylhexyl acrylate, and/or ethylenicallyunsaturated dicarboxylic acid esters or derivatives thereof, such asdiisopropyl fumarate and the dimethyl, dibutyl and diethyl esters ofmaleic acid or fumaric acid, or maleic anhydride. The choice from themonomers mentioned is preferably taken here such that copolymers havinga glass transition temperature T_(g) of -30° C. to +30° C. are obtained.

The (meth)acrylic acid ester copolymers can comprise, if appropriate,1.0 to 50% by weight, based on the total weight of the comonomer phase,of α-olefins, such as ethylene or propylene, and/or vinylaromatics, suchas styrene, and/or vinyl halides, such as vinyl chloride, and/orethylenically unsaturated dicarboxylic acid esters or derivativesthereof, such as diisopropyl fumarate and the dimethyl, dibutyl anddiethyl esters of maleic acid or fumaric acid, or maleic anhydride. Thechoice from the monomers mentioned is preferably taken here such thatcopolymers having a glass transition temperature T_(g) of -30° C. to+30° C. are obtained.

If appropriate, the vinyl ester copolymers and the (meth)acrylic acidester copolymers also comprise 0.05 to 3.0% by weight, based on thetotal weight of the comonomer mixture, of one or more auxiliary monomersfrom the group consisting of ethylenically unsaturated carboxylic acids,preferably acrylic acid or methacrylic acid, from the group consistingof ethylenically unsaturated carboxylic acid amides, preferablyacrylamide and 2-acrylamidopropanesulfonic acid, from the groupconsisting of ethylenically unsaturated sulfonic acids and saltsthereof, preferably vinylsulfonic acid, and/or from the group consistingof poly-ethylenically unsaturated comonomers, for example divinyladipate, 1,9-decadiene, allyl methacrylate and triallyl cyanurate, andcrosslinking comonomers, such as acrylamidoglycolic acid (AGA),methacrylamidoglycolic acid methyl ester (MAGME) and polyglycoldimethacrylate.

Preferred vinyl ester copolymers comprise as comonomer units a), in eachcase based on the total weight of the copolymer:

90 to 99.7% by weight of vinyl ester, in particular vinyl acetate;

49.7 to 89.7% by weight of vinyl ester, in particular vinyl acetate and10 to 50% by weight of α-olefin, in particular ethylene;

50 to 75% by weight of vinyl acetate, 1 to 30% by weight of vinyl esterof an α-branched carboxylic acid, in particular VeoVa9® and/or VeoVa10®,and 10 to 40% by weight of ethylene;

70 to 98.7% by weight of vinyl acetate and 1 to 30% by weight of vinylester of an α-branched carboxylic acid, in particular VeoVa9® and/orVeoVa10®,

70 to 98.7% by weight of vinyl ester, in particular vinyl acetate, and 1to 30% by weight of acrylic acid ester, in particular n-butyl acrylateor 2-ethylhexyl acrylate;

50 to 75% by weight of vinyl acetate, 1 to 30% by weight of acrylic acidester, in particular n-butyl acrylate or 2-ethylhexyl acrylate, and 10to 40% by weight of ethylene; or

30 to 75% by weight of vinyl acetate, 1 to 30% by weight of vinyl esterof an α-branched carboxylic acid, in particular VeoVa9® and VeoVa10®1 to30% by weight of acrylic acid ester, in particular n-butyl acrylate or2-ethylhexyl acrylate, and 10 to 40% by weight of ethylene.

Preferred (meth)acrylic acid ester copolymers comprise as comonomerunits a), in each case based on the total weight of the copolymer:

90 to 99.7% by weight of n-butyl acrylate and/or 2-ethylhexyl acrylate;

40 to 59.7% by weight of methyl methacrylate and 59.7 to 40% by weightof n-butyl acrylate and/or 2-ethylhexyl acrylate; or

40 to 59.7% by weight of styrene and 59.7 to 40% by weight of n-butylacrylate and/or 2-ethylhexyl acrylate.

The vinyl ester copolymers or the (meth)acrylic acid ester copolymersare preferably prepared by the emulsion polymerization process. Thepolymerization can be carried out discontinuously or continuously, withor without the use of seed lattices, with initial introduction of all orindividual constituents of the reaction mixture, or with partial initialintroduction and subsequent metering-in of the constituents orindividual constituents of the reaction mixture, or by the meteringprocess without an initial introduction. All the meterings arepreferably effected at the rate of consumption of the particularcomponent.

In a preferred embodiment, 10 to 25% by weight of comonomers a) areinitially introduced and the remainder is metered in as emulsiontogether with comonomers b). Copolymerization with ethylene ispreferably carried out under a pressure of 20 to 100 bar absolute.

The polymerization is carried out in a temperature range from 40° C. to80° C. and is initiated using the methods usually employed for emulsionpolymerization. The initiation is effected by means of the customarywater-soluble agents which form free radicals, which are preferablyemployed in amounts of 0.01 to 1.0% by weight, based on the total weightof the monomers. Examples of these are ammonium and potassiumpersulfate, alkyl hydroperoxides, such as tert-butyl hydroperoxide, andhydrogen peroxide. If appropriate, the free radical initiators mentionedcan also be combined in a known manner with 0.01 to 0.5% by weight,based on the total weight of the monomers, of reducing agents. Suitablereducing agents are, for example, formaldehyde-sulfoxylate salts, sodiumbisulfite or ascorbic acid. In the case of redox initiation, one or bothredox catalyst components are preferably metered in during thepolymerization.

Dispersing agents which can be employed are all the emulsifiers andprotective colloids usually used in emulsion polymerization. Preferably,1 to 4% by weight, based on the total weight of the monomers, ofemulsifier are employed. Examples of suitable emulsifiers are anionicsurfactants, such as alkyl sulfates having a chain length of 8 to 18 Catoms, alkyl- and alkylaryl ether sulfates having 8 to 18 C atoms in thehydrophobic radical and up to 40 ethylene oxide or propylene oxideunits, alkyl- or alkylarylsulfonates having 8 to 18 C atoms, and estersand half-esters of sulfosuccinic acid with monohydric alcohols oralkylphenols. Suitable nonionic surfactants are, for example, alkylpolyglycol ethers or alkylaryl polyglycol ethers having 8 to 40 ethyleneoxide units.

If appropriate, protective colloids can be employed, preferably inamounts of up to 4% by weight, based on the total weight of themonomers. Examples of these are vinyl alcohol/vinyl acetate copolymershaving a content of 80 to 100 mol % of vinyl alcohol units,polyvinylpyrrolidones having a molecular weight of 5000 to 400,000, andhydroxyethylcelluloses having a degree of substitution in the range from1.5 to 3.

The pH range desired for the polymerization, which is in general between3 and 7, can be established in a known manner by acids, bases orcustomary buffer salts, such as alkali metal phosphates or alkali metalcarbonates. To establish the molecular weight, the regulators usuallyused, for example mercaptans, aldehydes and chlorinated hydrocarbons,can be added during the polymerization.

The solids content of the aqueous dispersions is preferably 30 to 65% byweight.

To prepare the dispersion powders, the dispersion is dried, preferablyspray dried or freeze dried, particularly preferably spray dried. Theknown devices, such as, for example, spraying through multi-componentnozzles or with a disc, in a stream of dry gas, which is heated ifappropriate, can be used for this procedure. Temperatures above 250° C.are in general not used. The optimum temperature of the dry gas can bedetermined in a few experiments; temperatures above 60° C. have oftenproved to be particularly suitable.

To increase the storage stability and, for example in the case ofpowders of low glass transition temperature T_(g), to prevent caking andblocking, an antiblocking agent, for example aluminum silicates,kieselguhr or calcium carbonate, is added, if appropriate, during thedrying. It is furthermore also possible to add to the dispersion, ifappropriate, defoamers, for example based on silicones or hydrocarbons,or spraying aids, for example polyvinyl alcohols or water-solublemelamine-formaldehyde condensation products.

In a preferred embodiment, the dispersion powders also comprise 0 to 30%by weight, particularly preferably 1 to 15% by weight, based on the basepolymer, of polyvinyl alcohol having a degree of hydrolysis of 85 to 94mol %, and/or 0 to 10% by weight of vinyl alcohol copolymers with 5 to35% by weight of 1-methylvinyl alcohol units, and/or 0 to 30% by weight,particularly preferably 4 to 20% by weight, based on the total weight ofpolymeric constituents, of antiblocking agent, and, if appropriate, upto 2% by weight, based on the base polymer, of defoamer.

The aqueous copolymer dispersions and the redispersible dispersionpowders are suitable for finishing and bonding of naturally occurring orsynthetic fiber materials. Examples of these are wood fiber, cellulosefiber, wool, cotton, mineral fibers, ceramic fibers and synthetic fibersbased on fiber-forming polymers, such as viscose fiber, polyethylene,polypropylene, polyester, polyamide, polyacrylonitrile or carbon fiber,fibers of homo- or copolymers of vinyl chloride or fibers of homo- orcopolymers of tetrafluoroethylene. The aqueous copolymer dispersions andthe dispersion powders are particularly suitable for finishing andbonding of cellulose fiber materials.

The invention furthermore relates to a process for the preparation ofsolvent-resistant fiber structures, which comprises applying an aqueouscopolymer dispersion or a redispersible copolymer powder of copolymershaving a T_(g) of -60° C. to +60° C. comprising

a) one or more monomer units from the group consisting of vinyl estersof unbranched or branched carboxylic acids having 1 to 12 C atoms,esters of acrylic acid and methacrylic acid with unbranched or branchedalcohols having 1 to 12 C atoms, vinylaromatics, vinyl halides andα-olefins and

b) 0.3 to 10% by weight, based on the total weight of the copolymer, ofa mixture of one or more N-(alkoxymethyl)acrylamides orN-(alkoxymethyl)methacrylamides with a C₁ - to C₆ -alkyl radical withN-methylolacrylamide and/or N-methylolmethacrylamide in a weight ratioof N-methylol compound to

N-(alkoxymethyl) compound of not more than 5:1, in an amount of 5 to 50%by weight of binder, based on the fiber weight, to the fiber materialspread out in a flat form, and drying at a temperature of 80° to 200° C.

Before the bonding, the fibers are spread out in a flat form. Theprocesses for this are known and depend primarily on the use to whichthe bonded fiber material is put. The fibers can be laid out by means ofan air laying, wet laying, direct spinning or carding device. Ifappropriate, the flat structures can also be bonded mechanically beforethe bonding with the binder, for example by cross-laying,needle-punching or water jet bonding.

When used according to the invention, the aqueous copolymer dispersionsare applied in the customary manner by impregnation, foam impregnation,spraying, slop padding, brushing or printing. If appropriate, afterremoval of excess binder by, for example, squeezing off, the textilestructures are dried at temperatures of 80° to 200° C., preferablybetween 120° and 180° C. The amount of binder needed for bonding thefiber material is between 5 and 50% by weight of binder, based on thefiber weight, depending on the field of use.

If copolymer powders are used, in a manner known per se the pulverulentbinder is sprinkled onto, sprinkled into (for example in the case ofcarded wadding) or compacted by vibration into the fiber material, whichis prebonded mechanically if appropriate, or mixed directly with thefiber. The textile structures are dried at temperatures of 80° to 200°C., preferably between 120° and 180° C. The amount of binder needed forbonding the fiber material is between 5 and 50% by weight, based on thefiber weight, depending on the field of use.

Pigments, antioxidants, dyestuffs, plasticizers, film-formingauxiliaries, fillers, flameproofing agents, foam formation auxiliaries,foam inhibitors, wetting agents, heat sensitization agents, antistatics,biocides, agents which improve handle, additional crosslinking agents orcatalysts for any necessary acceleration of the crosslinking reactioncan also be added to the binder according to the invention in theamounts customary for this purpose.

The solvent-resistant textile binder is preferably suitable for bondingnonwovens, for example in the domestic and hygiene sector, and forindustrial wiping cloths. Another field of use is non-slip finishing ofwoven fabrics.

The following examples serve to illustrate the invention further:

Preparation of the Copolymer Dispersions

EXAMPLE 1

192 kg of water, 1.46 kg of a 10% strength aqueous formic acid solution,14.7 kg of an aqueous solution of an isotridecyl ethoxylate with 15 EOunits (Genapol X150) and 2.02 kg of a 25% strength aqueous solution ofvinyl sulfonate were initially introduced together with 27.3 g of butylacrylate and 17.6 kg of vinyl acetate into a pressure reactor. Themixture was heated up to 50° C. and ethylene was forced in under apressure of 60 bar. When temperature equilibrium had been reached, asolution of 619 g of ammonium persulfate in 24.2 kg of water and asolution of 309 g of ascorbic acid in 24.5 kg of water were metered in.After the initial mixture had polymerized completely, 187 kg of vinylacetate were metered in. After the end of the metering of vinyl acetate,a mixture of 12.6 kg of water, 10.5 kg of a 30% strength aqueousacrylamide solution, 2.4 kg of N-methylolacrylamide and 2.4 kg ofN-(isobutoxymethyl)acrylamide, together with a mixture of 16.7 kg ofbutyl acrylate and 16.7 kg of vinyl acetate, was metered in. When thepolymerization had ended, a dispersion having a solids content of 53% byweight and a copolymer composition of 11.0% of ethylene, 72.0% of vinylacetate, 14.2% of butyl acrylate, 1.0% of acrylamide, 0.8% ofN-methylolacrylamide and 0.8% of N-(isobutoxymethyl)acrylamide and 0.2%of vinyl sulfonate resulted.

Example 2 (Comparison Example)

The procedure was analogous to Example 1, with the difference thatinstead of the NMA/IBMA mixture, 4.8 kg of N-(isobutoxymethyl)acrylamidewere copolymerized.

When the polymerization had ended, a dispersion having a solids contentof 53% by weight and a copolymer composition of 11.0% of ethylene, 72.0%of vinyl acetate, 14.2% of butyl acrylate, 1.0% of acrylamide, 1.6% ofN-(isobutoxymethyl)acrylamide and 0.2% of vinyl sulfonate resulted.

Example 3 (Comparison Example)

The procedure was analogous to Example 1, with the difference that onlyN-methylolmethacrylamide and no N-(isobutoxymethyl)acrylamide was used.

After the end of the polymerization, a dispersion having a solidscontent of 53% by weight and a copolymer composition of 11.0% ofethylene, 72.0% of vinyl acetate, 14.2% of butyl acrylate, 1.0% ofacrylamide, 1.6% of N-methylolacrylamide and 0.2% of vinyl sulfonateresulted.

Example 4

542 g of water, 0.5 g of a 10% strength aqueous Fe(II) sulfate solution,11.9 g of an aqueous solution of an ethylene oxide/propylene oxide blockcopolymer (Genapol PF40) and 3.1 g of a 25% strength aqueous solution ofvinyl sulfonate, together with 8.2 g of butyl acrylate and 70.5 g ofvinyl acetate, were initially introduced into a laboratory reactor. Themixture was heated up to 45° C. When temperature equilibrium had beenreached, a solution of 9.8 g of ammonium persulfate in 187 g of waterand a solution of 4.9 g of Rongalite in 192 g of water were metered in.After the initial mixture had polymerized completely, 776 g of vinylacetate and 39.6 g of butyl acrylate were metered in. When the meteringof the vinyl acetate/butyl acrylate had ended, a mixture of 86 g ofwater, 9.21 g of acrylic acid, 20.7 g of N-methylolacrylamide and 9.9 gof N-(isobutoxymethyl)acrylamide, together with 76.8 g of a 40% strengthaqueous solution of an isotridecyl ethoxylate with 15 EO units (GenapolX150) and 21.9 g of a 28% strength aqueous solution of a sulfated alkylethoxylate with about 3 EO units (Genapol ZRO), was metered in.

When the polymerization had ended, a dispersion having a solids contentof 50% by weight and a copolymer composition of 91.0% of vinyl acetate,5.1% of butyl acrylate, 1.7% of N-methylolacrylamide, 0.8% ofN-(isobutoxymethyl)acrylamide, 1.0% of acrylic acid and 0.01% of vinylsulfonate resulted.

Example 5 (Comparison Example)

The procedure was analogous to Example 4, with the difference that onlyN-methylolmethacrylamide and no N-(isobutoxymethyl)acrylamide was used.

When the polymerization had ended, a dispersion with a solids content of50% by weight and a copolymer composition of 91.0% of vinyl acetate,5.1% of butyl acrylate, 2.5% of N-methylolacrylamide, 1.0% of acrylicacid and 0.01% of vinyl sulfonate resulted.

Use Tests

Production of the Nonwovens

To produce the nonwovens, a viscose staple fiber nonwoven was bondedwith 20% by weight of copolymer dispersion (solids, based on the fiber)by means of full bath impregnation. The excess binder was squeezed offbetween two rolls and the nonwoven was dried in a drum drier at 150° C.for 3 minutes.

Determination of the Strength of the Nonwovens in Accordance with DIN53857

The dry strength, wet strength and resistance to solvents of thenonwovens was determined by means of measurement of the maximum tensileforce (MTF) of strips of nonwoven with a width of 1.5 cm and a length of15 cm. Before the measurement, the nonwovens were kept in a standardclimate at T=23° C. and 50% relative atmospheric humidity (DIN 50014)for at least 24 hours.

To determine the wet strength, the nonwovens were kept in water for 1minute immediately before the measurement. To determine the resistanceto solvents, the nonwovens were kept in isopropanol for 1 minuteimmediately before the measurement.

The maximum tensile force was measured with a Zwick tensile tester, thetensile measurement being carried out at a constant rate of elongationof 100 mm/minute. For each measurement, the maximum tensile force isdetermined and the measurement is ended when the force has fallen to 40%of the maximum tensile force. In each case 5 strips of nonwoven perspecimen were clamped jointly. The mean of two measurement series wasdetermined.

The results of the measurements are summarized in Table 1:

                  TABLE 1                                                         ______________________________________                                               NMA     IBMA    MTF (N) MTF (N)                                                                              MTF (N)                                 Example                                                                              (%)     (%)     dry     wet    isopropanol                             ______________________________________                                        1      0.8     0.8     20.4    9.5    8.5                                     2*     0       1.6     19.1    8.4    8.1                                     3*     1.6     0       19.1    9.2    5.1                                     4      1.7     0.8     25.5    11.3   13.3                                    5*     2.5     0       23.0    10.2   10.0                                    ______________________________________                                         *Comparison examples                                                     

We claim:
 1. A process for improving the resistance to solvents of fibermaterials bonded or coated with an aqueous copolymer dispersion or aredispersible powder, which comprises finishing and bonding the fibermaterials with an N-(alkoxymethyl) (meth)acrylamide-functional textilebinder comprised of an aqueous copolymer dispersion or a redispersiblecopolymer powder of copolymers having a T_(g) of -60° C. to +60° C.comprisinga) one or more monomer units selected from the groupconsisting of vinyl esters of unbranched carboxylic acids having 1 to 12C atoms, esters of acrylic acid and methacrylic acid with unbranched orbranched alcohols having 1 to 12 C atoms, vinylaromatics, vinyl halidesand α-olefins and b) 0.3 to 10% by weight, based on the total weight ofthe copolymer, of a mixture of monomer units of one or moreN-(alkoxymethyl)acrylamides or N-(alkoxymethyl)methacrylamides havingC₁ - to C₆ - atoms in the alkoxy radical with N-methylolacrylamideand/or N-methylolmethacrylamide in a weight ratio of the N-methylolcompound to the N-(alkoxymethyl) compound of not more than 5:1.
 2. Theprocess as claimed in claim 1, wherein the copolymer comprises 0.5 to3.0% by weight, based on the total weight of the copolymer, of a mixtureof N-(alkoxymethyl) (meth)acrylamides with N-methylolacrylamide orN-methylolmethacrylamide in a weight ratio of N-methylol compound toN-(alkoxymethyl) compound of 5:1 to 1:10.
 3. The process as claimed inclaim 1 wherein the copolymer is selected from the group consisting ofN-(isobutoxymethyl)acrylamide (IBMA), N-(isobutoxymethyl) methacrylamide(IBMMA), N-(n-butoxy-methyl)acrylamide (NBMA) andN-(n-butoxymethyl)methacrylamide (NBMMA) as N-(alkoxymethyl)(meth)acrylamides.
 4. The process as claimed in claim 3, wherein thecopolymer comprises 0.5 to 3.0% by weight, based on the total weight ofthe copolymer, of a mixture of N-methylolacryl amide (NMA) and eitherN-(isobutoxymethyl)acrylamide (IBMA) orN-(isobutoxymethyl)methacrylamide (IBMMA) wherein the weight ratio ofNMA/IBMA (IBMMA) is 3:1 to 1:5.
 5. The process as claimed in claim 1wherein the vinyl ester copolymer of comonomer units a), in each casebased on the total weight of the copolymer, is selected from the groupconsisting of:(1) 90 to 99.7% by weight of vinyl ester; (2) 49.7 to89.7% by weight of vinyl ester, and 10 to 50% by weight of an α-olefin;(3) 50 to 75% by weight of vinyl acetate, 1 to 30% by weight of vinylester of an α-branched carboxylic acid, and 10 to 40% by weight ofethylene; (4) 70 to 98.7% by weight of vinyl acetate and 1 to 30% byweight of vinyl ester of an α-branched carboxylic acid; (5) 70 to 98.7%by weight of a vinyl ester, and 1 to 30% by weight of an acrylic acidester; (6) 50 to 75% by weight of vinyl acetate, 1 to 30% by weight ofacrylic acid ester, and 10 to 50% by weight of ethylene; and (7) 30 to75% by weight of vinyl acetate, 1 to 40% by weight of a vinyl ester ofan α-branched carboxylic acid, 1 to 30% by weight of an acrylic acidester, and 10 to 40% by weight of ethylene.
 6. The process as claimed inclaim 1 wherein a (meth)acrylic acid ester copolymer which comprises ascomonomer units a), in each case based on the total weight of thecopolymer, is a member selected from the group consisting of 90 to 99.7%by weight of n-butyl acrylate and/or 2-ethylhexyl acrylate; 40 to 59.7%by weight of methyl methacrylate and 59.7 to 40% by weight of n-butylacrylate and/or 2-ethylhexyl acrylate; and 40 to 59.7% by weight ofstyrene and 59.7 to 40% by weight of n-butyl acrylate and/or2-ethylhexyl acrylate.
 7. A process for the preparation of asolvent-resistant fiber structure, which comprises applying an aqueouscopolymer dispersion or a redispersible copolymer powder of copolymershaving a T_(g) of -60° C. to +60° C. comprisinga) one or more monomerunits selected from the group consisting of vinyl esters of unbranchedor branched carboxylic acids having 1 to 12 C atoms, esters of acrylicacid and methacrylic acid with unbranched or branched alcohols having 1to 12 C atoms, vinylaromatics, vinyl halides and α-olefins and b) 0.3 to10% by weight, based on the total weight of the copolymer, of a mixtureof one or more N-(alkoxymethyl)acrylamides orN-(alkoxymethyl)methacrylamides having C₁ - to C₆ -atoms in the alkoxyradical with N-methylolacrylamide and/or N-methylolmethacrylamide in aweight ratio of N-methylol compound to N-(alkoxymethyl) compound of notmore than 5:1,in an amount of 5 to 50% by weight of binder, based on thefiber weight, to the fiber material spread out in a flat form, anddrying at a temperature of 80° to 200° C.
 8. The solvent resistant fiberstructure prepared by the process of claim
 7. 9. The process of claim 5wherein in (1), (2) and (5), the vinyl ester is vinyl acetate.
 10. Theprocess of claim 5 wherein in (2), the α-olefin is ethylene.
 11. Theprocess of claim 5, wherein in (3), (4) and (7), the α-branchedcarboxylic acid is a mixture of C₁₀ saturated monocarboxylic acidisomers.
 12. The process of claim 5, wherein in (3), (4) and (7), theα-branched carboxylic acid is a mixture of C₉ saturated monocarboxylicacid isomers.
 13. The process of claim 5 wherein in (6) and (7), theacrylic acid ester is N-butyl acrylate or 2-ethylhexyl acrylate.